1. Field of the Invention
This invention relates to an apparatus for the treatment of a low-concentration organic waste water, which in a system for recovering ultra pure water for use in the production of semiconductor devices, for example, renders the low-concentration organic waste water originating in the point of use and having a T0C (total organic carbon) concentration of the order of ppm reusable for the production by divesting the waste water of its organic content until a TOC concentration of not more than 1 ppb.
2. Description of the Related Arts
Heretofore, in the process of production of semiconductor devices, ultra pure water has been used in large volumes for washing semiconductor wafers. The low-concentration waste water arising from the point of use is subjected to a reclaim treatment in a recovery system for the purpose of reuse.
The waste water from the point of use entrains volatile organic compounds such as those cited below, for example, on the order of ppm. For reuse in the process of production of semiconductor devices, this waste water must be purified to a TOC concentration of not more than 1 ppb.
______________________________________ Isopropanol 1120.1 ppb 1,1-Dichloroethylene 0.3 ppb Cis-1,2-dichloroethylene 9.1 ppb Chloroform 0.4 ppb Trichloroethylene 14.5 ppb Bromodichloromethane 0.2 ppb Tetrachloroethylene 0.5 ppb Dibromochloromethylene 0.3 ppb ______________________________________
The large volume of isopropanol content among other TOC contents in the waste water is because the vapor of isopropanol is used for drying the washed semiconductor wafers.
Heretofore, treatment of the low-concentration organic waste water, utilized a high-pressure ultraviolet lamp for decomposing by oxidation the TOC in the waste water. This method comprised adding hydrogen peroxide to the waste water containing TOC and irradiating the waste water with an ultraviolet light having main wavelengths of 365 nm 253.7 nm and emitted from the high-pressure ultraviolet lamp thereby decomposing the TOC in the waste water by oxidation. The inorganic carbon and organic acids arising from the decomposition of TOC and the excess hydrogen peroxide remaining after the treatment are then removed by an activated carbon column, an ion-exchange resin column, and a reverse osmosis unit.
However, the high-pressure ultraviolet lamp used for this method is expensive. Furthermore, decomposition is enefficient in regards to the amount of electric power consumed, resulting in an unduly long time spent for the irradiation. Also, the tank used for the treatment requires a large capacity and occupies a large space. Further, since a fairly large part of the electric power consumed is transformed into heat energy, the treatment under consideration entails copious generation of heat energy thereby boosting the running costs. If the flow of the waste water stops, the possibility may ensue that the heat will quickly raise the temperature of the waste water in the tank and set the waste water boiling. An additional disadvantage is the activated carbon column tends to induce propagation of contaminants. The method which treats the low-concentration organic waste water with the conventional apparatus for producing ultra pure water by the use of the high-pressure ultraviolet lamp, therefore, incurs the problem of entailing a high initial cost and a high running cost.
As a way of treating the low-concentration organic waste water without recourse to a high-pressure ultraviolet lamp, the method which biologically implements the decomposition of the TOC in the waste water under treatment by passing the waste water through a treating column having aerobic microorganisms propagated therein has been known. This method, however, encounters the problem of demanding very exacting management of equipment because its treating ability is susceptible to serious impairment when contaminants enter the treating column.
Further, MICROCONTAMINATION 92 Conference Proceedings, October, Santa Clara, pp. 729-738 discloses at page 736 what is titled "BEST AVAILABLE TECHNOLOGY TO MEET CURRENT SEMICONDUCTOR MANUFACTURING REQUIREMENT." By the system illustrated therein, a given raw water is transformed into extremely purified water by treatments using many unit devices such as a reverse osmosis unit, a degasifier, an ultraviolet irradiating unit, and an ion-exchange resin column.
This system, however, must use many unit devices and has never been reviewed from the standpoint of decreasing the number of indispensable unit devices to the fullest possible extent.